This invention directed to the field of elongated intraluminal devices having surfaces with lubricious coatings, and, in particular, to a low friction guidewire having an improved distal tip design.
Guidewires are well known in the art and have been the subject of continual improvement. One direction of improvement has centered on reducing the surface friction of the guidewire to facilitate insertion and advancement of the guidewire and the subsequent introduction of a vascular device threaded over it. Much of the innovation has centered on laminating a low friction, polymeric material onto the surface of the guidewire. Polytetrafluoroethylene (PTFE) and various hydrophilic polymers, such as polysiloxane, are examples.
In addition to guidewires, virtually all intraluminal devices may benefit from having a lubricious surface to facilitate insertion and guidance to the desired intraluminal destination. Reducing friction also minimizes luminal trauma caused by insertion of these devices, particularly in blood vessels such as coronary arteries. Often, multiple intraluminal devices are used during a procedure such as angioplasty or atherectomy, requiring coaxial or rotational movement with respect to each other. In such instances, the outer surface of the device, whether it interacts with the interior of another intraluminal device or the vasculature, and device lumens that receive other intraluminal devices are candidates for a lubricious surface. As with guidewires, much has been done with the prior art polymer layers to produce intraluminal devices having low friction surfaces. Although the prior art has achieved certain successes, a number of drawbacks are associated with the use of polymer layers. Generally, elongated intraluminal devices are quite long and have a small outer diameter. For example, a typical guide wire is 175 cm long, but can be 300 cm or longer, and has an outer diameter of between 0.010 and 0.050 inch. Providing such devices with a uniform coating is technically difficult and correspondingly expensive. Further, intraluminal devices having layers comprising polymeric materials require extreme care in handling as the layers are very susceptible to abrasion and other damage.
There remains a need for intraluminal devices having a tenacious effective lubricious surface without the drawbacks associated with the prior art techniques. In particular, there is a need for a low friction guidewire with an improved distal tip. This invention satisfies these and other needs.
This invention is directed to elongated intraluminal devices that have a tenacious lubricious coating on their surface comprising a finely divided lubricious particulate. The lubricious particulate is preferably selected from the group consisting of tungsten disulfide, molybdenum disulfide and the like. The coatings of this invention have a thickness of not more than about 0.00002 inch and generally form a monomolecular layer. Preferably, the coefficient of friction is not more than about 0.030. The coatings also have a hardness not less than about 1.0 Mohs. Preferably, the surface coating comprises a monomolecular layer of particulate tungsten disulfide. The lubricious particulate is preferably not more than about 0.5 micron in maximum diameter.
The coatings of this invention offer significantly improved characteristics over the prior art polymer coatings. One significant advantage is that the lubricious particulate coatings are much thinner than the polymer coatings. Preferably, the lubricious particulates form an irreversible bond with the substrate but do not bond each other. Accordingly, they form a very uniform monomolecular layer. Since the particulate coatings are tenacious and relatively hard, they are more durable than typical polymeric coatings. The particulate coatings also offer at least equivalent coefficients of friction as the polymeric coatings.
In addition to the tenacious lubricious particulate surface coating, the guidewires of this invention incorporate an improved distal tip configuration designed to maximize flexibility while maintaining torsional and columnar strength. The guidewire comprises a flexible elongate core member that has at least one tapered section at its distal extremity and a flattened distal portion. The distal portion has two or more flattened regions having cross-sectional areas which decrease in the distal direction. The maximum diameter of the guidewire is not more than about 0.03 inch, and preferably is not more than about 0.015 inch.
A flexible helical coil of suitable material wraps around and is attached to the core member. The helical coil comprises three or more distinct regions, each having increasing coil spacing in the distal direction to provide correspondingly greater flexibility. The most distal region of the coil is secured to the distal portion by suitable means, such as solder, to form a rounded plug at the distal tip. The most proximal end of the coil is secured to the core member by suitable means such as solder.
This distal tip configuration with variable coil spacing provides a smooth transition from a relatively stiff proximal section to a very flexible distal section while maintaining adequate columnar and torsional strength. The rectangular cross sections of the flattened distal portion bias the flexibility of the coil in the direction normal to the major dimension of the rectangular cross section.
Preferably, the entire length of the guidewire proximal to the helical coil has the lubricious particulate surface coating of the invention. In others, a portion of the guidewire proximally adjacent the helical coil may have an additional layer of a conventional lubricious polymer under the lubricious particulate coating.